Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

The best way to do this is by checking your superheated at the compressor.
Depending on how far the compressor is from the case or box, the condition of the insulation on the suction line and were the pipe is ran ( overhead under the roof or underground).
This is why superheated does not matter. What matters is the proper cooling of the compressor. I had to work with several systems where the superheat needed to be set to 1 df in order to provide proper cooling to the compressor
Check your comp specs. It's usually 60-65 df max suction line temp at compressor on the medium temp and 25df on low temp

This is why superheated does not matter. What matters is the proper cooling of the compressor.

Superheat at the coil is VERY important. Imagine you have a system with a long piping run in a ceiling under a roof. On a sunny hot day, you check compressor superheat and find it too high. To compensate, you open the TXV farther. Now compressor superheat is good. However, you may have just set the valve to 0 degrees superheat and are feeding liquid into the suction line. Under the current operating conditions this is OK because it al vaporizes before getting to the compressor. However, as soon as the temp in the ceiling drops, the load on the line is going to go down and you will have floodback.

Its important to set the TXV at the superheat recommended for the application, then verify the superheat at the compressor is within manufacturers recommendations. If it is too high it should be addressed with additional insulation, a desuperheating valve, or other measures.

The best way to do this is by checking your superheated at the compressor.
Depending on how far the compressor is from the case or box, the condition of the insulation on the suction line and were the pipe is ran ( overhead under the roof or underground).
This is why superheated does not matter. What matters is the proper cooling of the compressor. I had to work with several systems where the superheat needed to be set to 1 df in order to provide proper cooling to the compressor
Check your comp specs. It's usually 60-65 df max suction line temp at compressor on the medium temp and 25df on low temp

I will respectfully disagree with your position here.

The TEV is not designed to regulate superheat at a location that is downstream from the sensing bulb location. It is impossible for any valve requiring temperature and pressure to regulate its adjustment to maintain a condition somewhere other than where it is sensing temperature and pressure at.....that would be the height of lunacy to expect a valve to regulate at some location in the system other than where it is sensing the condition it is attempting to regulate.

In addition, there are so many variables (load, ambient conditions, etc) that will change the refrigerant mass flow requirement necessary to properly feed the evaporator that what might seem to be a decent compressor superheat at one operating condition might be extremely low at another....again, the TEV is not designed to regulate superheat at a location other than the bulb location.

To repeat.....the TEV is designed to maintain superheat at the bulb location only. Once this is set correctly, IF the compressor superheat is too high it must be addressed in another manner such as liquid injection.